Electric power daily used by users is generated by various power stations (e.g., nuclear, thermal, and hydroelectric power stations), and high-quality electric power is stably supplied to consumers through trunk transmission power systems and distribution systems. However, the existing power systems use large-scale centralized power plants in order to stably supply large amounts of electricity. This prolongs the lead time from planning to the start of operation. Also, areas meeting the conditions of locations for large-scale power plants are often far from demand areas. This limits increases in the total energy efficiency, which includes the heat collection rate.
Also, as concern for environmental protection increases and relevant laws are enforced in recent years, a demand for environmental load reduction such as CO2 reduction is increasing. To meet this demand, the development and implementation of renewable energies such as fuel cells, biomass power generation, solar power generation, wind power generation, and thermal storage devices are rapidly advancing. On the other hand, outputs from dispersed power sources using natural energy such as sunlight and wind are unstable and difficult to control. Therefore, when many dispersed power sources using natural energy are connected to the existing large-scale power networks (to be referred to as “commercial networks” hereinafter) in the future, these power sources may adversely affect qualities such as the stability and reliability of the system.
As a means for solving these problems, smart grids and micro grids are recently attracting much attention throughout the world. For example, a micro grid can achieve a high total energy efficiency by placing a power source in a demand area. It is also possible to construct a network that does not influence the commercial network while taking account of the environment, by using a power source configuration combining a power source such as a naturally varying power source that is difficult to control and a controllable power source. A “micro grid” is termed a “good citizen” as it comprises small-scale networks and systems of dispersed power sources by mutually compensating for the features of these dispersed power sources, thereby minimizing the influence on power systems and contributing to the power systems.
Much research and demonstration of micro grids has taken place in Japan as well. In a project from 2003 to 2007, empirical research undertaken at the behest of the NED was carried out in, e.g., Aichi, Kyoto, and Hachinohe. It is anticipated that micro grids will contribute in dealing with issues such as peaks in power demand and load leveling, in addition to environmental problems. The contents of many reports concerning micro grids relate to evaluations pertaining to the balancing of the connection point flow which takes into account smooth operation in normal operation, or demand/supply control functions of balancing the demand and supply by using, e.g., dispersed power sources and power storage devices.
To actually operate a micro grid, it is necessary to perform monitoring and control to maintain the same power quality level as that of a commercial network. For example, it is necessary to perform all of demand/supply planning and frequency control performed by the EMS (Energy Management System), charge/blackout monitoring, system operation, fault restoration, and voltage control performed by the DAS (Distribution Automatic System), facility management, construction planning, and building work assistance performed by the DMS (Distribution Management System), and load control performed by the DSM (Demand Side Management).
The power source capacity of the existing commercial network (distribution system level) guarantees a power amount with which one power source terminal can supply electric power to the whole distribution line, except for, e.g., a demand peak time in summer. Even when system switching is performed because a fault has occurred or a work has to be performed, another power source can easily be secured, and the frequency at which a supply hindrance section occurs is very low. In the micro grid, however, the energy source is an aggregate of small dispersed power sources. Accordingly, even when the supply power amount is sufficient in normal operation, it is highly likely that sections in which the supply power amount becomes insufficient are produced in some places if system switching is performed. Therefore, many supply hindrance sections may be created in a micro grid even if the conventional power interchange method, which is based on the assumption that the power source capacity is sufficiently ensured, is utilized in the micro grid.
In an abnormal occasion such as when a fault has occurred, for example, the power generation outputs of dispersed power sources connected in the micro grid must be varied in order to secure the reserve capacity as an emergency measure. Even when the power generation outputs of the dispersed power sources are adjusted, however, it is sometimes impossible to ensure a sufficient supply power source amount because the power generation capacity is low, or there is a dispersed power source such as solar power generation or wind power generation whose power generation output is uncontrollable.
Also, when planning a work, a work performing system must be made by planning the adjustment of the power generation outputs of dispersed power sources and the demand loads. When performing the work, the same operation state as that in normal operation must be maintained. However, the micro grid includes a naturally varying power source (e.g., wind power generation or solar power generation) that varies the power generation output amount in accordance with, e.g., the weather of the day. Accordingly, a system state assumed when planning the work and that when performing the work are often different.
This problem arises not only in the micro grid but also in the smart grid.
In the above circumstances, it is desired to provide an executive monitoring and control system capable of appropriately interchanging electric power when a fault has occurred or when a work has to be performed in the smart grid or micro grid.